1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic apparatus, information recording apparatus or the like.
2. Description of Related Art
Conventionally the image forming apparatus of this type is adapted to store in a toner collecting box, toner to be discarded (hereinafter referred to as toner waste) which is collected by a cleaning unit from the surface of a photoconductive drum after image transfer and thence before the toner collecting box becomes full, it must be detected timely by proper detecting means so that the toner waste may be discarded from the apparatus.
If the capacity of the toner collecting box is set regardless of the service life of the photoconductive drum, disposal of the toner waste and exchange of the photoconductive drums are carried out at different times, resulting in more frequent maintenance services being needed.
To avoid such a problem, it is preferable that the toner collecting box is adapted to become full just as the photoconductive drum ends its service life.
Recently, there are increasing instances where images of photographs or other graphic originals are transferred. The volume of toner to be used varies significantly depending on the frequencies of transfer of the graphic originals. Accordingly, it is impracticable to arrange the toner collecting box to become full simultaneously with the expiry of the service life of the photoconductive drum.
If the capacity of the toner collecting box should be designed such that the toner collecting box becomes full just as the photoconductive drum ends its service life under given operational conditions, the toner collecting box would often become full before exchanging the photoconductive drums because the use of toner is within a range of normal operations but beyond the range of the aforesaid given operational conditions. Additionally, there are some actual cases where the volume of toner collected by a toner collector is abnormally large due to the occurrence of some abnormality.